This invention relates to a recording apparatus of thermal transfer type in which a carrier such as a transfer film carrying a thermally transferable recording material is used for thermal transfer recording of information on a recording medium. More particularly, this invention relates to an aforementioned apparatus based on a density tone recording method suitable for recording of character and pattern information of high image quality at a high speed.
In a prior art recording apparatus of thermal transfer type, a carrier such as a transfer recording film having a coating of thermally transferable ink on a base is used for recording information on a recording medium such as a recording sheet, as disclosed in, for example, Japanese Patent Laid-open No. 59-42976 published on Mar. 9, 1984. The carrier and the recording medium are superposed on each other at a recording section including a thermal head and a platen roller each having substantially the same width as that of the recording medium that is, the width of the recording medium in a direction perpendicular to the direction in which the recording medium is transported through the recording section, and the thermal head is operated or energized according to a character and pattern information signal to selectively transfer the ink on the carrier onto the recording medium thereby recording the character and pattern information on the recording medium. In this transfer record mode, the character and pattern information corresponding to one line is recorded by energizing the thermal head while stopping the rotation of the platen roller and stopping the movement of the carrier and the recording medium. More particularly, the theremal head includes an array of heating resistance elements, each corresponding in size to one picture element, which are arranged in a row corresponding to one line of the picture elements disposed in the direction of the width of the recording medium, so that one line of picture elements are recorded at a time when the thermal head is depressed onto the platen roller.
Upon completion of recording of one line by the transfer of ink, the platen roller is driven to transport the carrier and the recording medium, superposed on each other, in the forward or normal direction by a distance corresponding to the line spacing. After the carrier and the recording medium have been advanced in the normal direction by the distance described above, the rotation of the platen roller is stopped, and the thermal head is energized to record character and pattern information of the next line by the transfer of ink. Such an operation is repeated to successively record character and pattern information on the recording medium. During this manner of recording, the transfer energy provided by the character and pattern information signal applied to the thermal head is controlled to control the density of transferred dots, that is, to control the so-called density tone of characters and patterns.
In such a prior art recording apparatus of thermal transfer type, it is difficult to determine the recording position with high accuracy since the recording position tends to change with a variation of the load of the platen roller. Further, when the platen roller is intermittently driven as in the case of the prior art apparatus, the picture element or dot has a shape analogous to a circular shape which is invariable. Therefore, attainment of a high density tone depends only on the transfer characteristic of the recording material coated on the carrier. Further, even when the thermal transfer energy applied to the thermal head is increased higher than a predetermined maximum level or decreased lower than a predetermined minimum level, the density will saturate and remain unchanged, and the desired improvement in the image quantity will be limited. Also, due to the intermittent drive of the platen roller and in view of the relation between the recording speed and the positioning of the recording section, a drive source operable at a high speed and capable of generating a high output is required, resulting in an increase in the power consumption and an increase in the noise.